3-D Hydrogeological model of the Marsaba-Feshkha region

This study summarizes an investigation in the Marsaba-Feshkha area with the aim of improving exploitation strategies of groundwater resources. Natural discharges of the catchment are the Feshkha springs (Fig.3.3.2-1). The 3-D hydrogeological model developed in the study area allows the identification of groundwater flow patterns (Fig.3.3.2-1), testing various exploitation schemes prior to their implementation and assessing the hydrological potential of the area, i.e., the amount of water that can be safely extracted. Its geographical area covers a surface of approximately 700 km2 located on the eastern slopes of the Judea anticlinorium (Fig.3.3.2-2) bordered in the west by the water divide running along the Hebron and Ramallah anticlines, the Jordan Valley and the Dead Sea in the east, the latitude line 140 in the north and the water divide between Ein Feshkha and Qane-Samar springs in the Judea Desert in the south (Fig.3.3.2-2). The study area can be defined as semi-arid to arid and suffers from acute shortage of freshwater. It is a part of the eastern drainage basin of the Judea and Samaria hills, and is one of the few locations where water resources can be utilized by capturing the freshwater flows before they reach the Dead Sea. Rainfall sharply decreases from 500-700 mm/yr along the western margins of the area to less than 100-150 mm/yr in the east, along the Dead Sea shore. Previous studies indicated that substantial amounts of freshwater penetrate the aquifer in the relatively rainy replenishment zones on the western part of the basin (the eastern margins of the Judea Mountains). The ground water flows east of the Dead Sea where it mixes with local brines (see chapter 3.1.4). An indication to this is the relatively high discharge of saline water in the Feshkha springs, which constitute the main outlet of the Cenomanian aquifers in this area. There is probably also some leakage of freshwater through the Rift fault into the basin-fill sediments in the area north to the Dead-Sea (Fig.3.3.2-2). Little information is available on the area as most of the wells that penetrate the relevant aquifers are located in two clusters separated by great distances (Jerusalem-Herodion area in the west and the Jericho-MizpeJericho area in the east (Fig.3.3.2-2; Table.3.3.2-1). The geology and hydrogeology of this area is complex and suffers from a serious lack of reliable and geographically spread data. Therefore, the work done in the construction of the model relies heavily on soft data (data not directly measurable) inferred from available information of the regional geology, on accepted concepts regarding the most probable flow patterns and on the main components of the water budget in the area.The difference in groundwater level between the western and eastern edges of the area is ca. 1,100 m over a distance of 30 km. This implies an average hydraulic gradient of about 3%, which is obviously very unlikely. In order to cope with this apparent discrepancy geological and structural elements were considered. The area was divided into a number of secondary basins, separated by low permeability flexures through which large drops in the groundwater head occur. Within each basin, the hydraulic gradient is relatively moderate. This is equivalent to assuming the existence of a number of groundwater "cascades" in the area.Obviously, a computational model that aims to simulate groundwater flow processes in such an area suffers from the acute lack of information. However, it may also help in screening the various concepts of flow patterns by testing the resulting flow fields that it produces. Keeping in mind the strong limitations imposed by the lack of information, the work carried out in this study included: structuring of the geological model, provision of hydrological data and new classification of the aquifer layers, determination of the 3-D computational grid in order to take into account the geological features, preparation of initial conditions (in the Lower and Upper Cenomanian layers), determination of the boundary conditions; selection of the calibration period, preparation of the pumping and rainfall data for the selected calibration period, running of the model for the calibration period and assessment of model performance. This sequence has been simulated many times. In the light of the results the process stopped when an adequate and satisfactory fit between measured and simulated ground-water head elevations was achieved. At the end of this process, the results obtained were believed to be a relatively reliable computational model that reproduces the aquifer response to meteorological events and to pumping regimes. Groundwater exploitation scenarios for this area were elaborated, comparisons between scenarios were made and finally, recommendations were suggested regarding the enhanced exploitation suggesting alternatives for the sustainable exploitation of the groundwater resources. Such development is of considerable importance considering the water agreements formulated between Israel, the Palestinian Authority and Jordan.